Layered double hydroxides (LDHs), also known as hydrotalcite, are one type of anionic layered materials. The general formula can be described as: [M2+1-xM3+x(OH)2]An−x/n.mH2O, in which the M2+ and M3 + are divalent and trivalent metal ions, respectively; An− is an anion. x is the molar fraction of M3+; m is the numbers of crystalline water. The chemical elements, compositions and ratios of the host layers, and the types and numbers of the interlayer guests can be tuned in a wide range, and thus a series of new materials with specific structures and properties can be obtained.
The previous patent (No. CN1994888A) has put forwards a new method for the preparation of LDHs in a clean way. In this method, bruciteis used as the raw material that is rich in China. The LDHs are synthesized under high-temperate hydrothermal condition by mixing the brucite with aluminum hydroxide. Based on the reaction mechanism, brucite can dissolve into Mg2+ ions under high temperature condition, and form the nucleation at the surface of the aluminum hydroxide. The as-used autoclave is the common paddle-like stirring reactor, which cannot remove the nucleation from the surface of the aluminum hydroxide. The nucleus thus has hindered the continuous reaction, and reduced the reaction rate and yield. The obtained LDHs particles usually present a large size and wide distribution. These disadvantages have largely restricted the applications of LDH materials.